This invention relates to an air balancing device for hanging a body to be carried by balancing a load of the body to be carried against a supply pressure to a cylinder.
Conventionally, as shown in the Unexamined Japanese Patent Publication No. 10-30609, an air balancing device is known in which a load of a body to be carried operates on a reaction force chamber partitioned by a diaphragm. Based on a pressure variance in a pressure chamber owing to a variance of the load, a main valve of the air balancing device is switched so that compressed air is supplied to a working chamber of a cylinder from a pressure source, or the working chamber is opened to the atmosphere, to control the pressure in the working chamber. Then, by balancing the load of the body to be carried with a working force in the cylinder, the body to be carried is hung.
However, in such a conventional device, the main valve does not open or close unless the volume of the working chamber is increased or decreased by overcoming sliding resistance of packing of the cylinder to slide a piston when the body to be carried is raised or lowered. Therefore, the operation for raising and lowering the body to be carried is heavy and difficult to be performed.
One object of the present invention is to provide an air balancing device which is easy to operate.
In order to attain the above object, the present invention provides an air balancing device for balancing a working force of a piston of a cylinder with a weight of a body to be carried, comprising a pressure regulating valve for adjusting a pressure in a supply/discharge passage to a pressure balanced against the weight of the body to be carried, the supply/discharge passage being connected to a working chamber of the cylinder for raising and lowering the body to be carried, the air balancing device further comprising
a control valve for increasing and decreasing a pressure in a control passage in accordance with a balance between the weight of the body to be carried and a working force in a reaction force chamber to which a pilot pressure is introduced from the control passage,
the pressure regulating valve comprising a pressure regulating chamber connected to the control passage via an opening/closing valve, a pilot chamber to which the pilot pressure from the control passage is constantly introduced, and a control chamber to which a pilot pressure from the supply/discharge passage is introduced, the pressure in the supply/discharge passage being adjusted to a pressure balanced against the weight of the body to be carried in accordance with a balance between a working force in the pressure regulating chamber and working forces in the pilot chamber and the control chamber.
The air balancing device may further comprise a leverage member rockably supported, to which the cylinder hanging the body to be carried is attached, wherein the pressure in said control passage is increased and decreased by bringing the working force in said reaction force chamber to operate on the leverage member to a direction counteracting the weight of the body to be carried, and also by opening and closing said control valve as a result of a rock of the leverage member. The air balancing device may further comprise a biasing member which is balanced with the weight of the cylinder.